An ultrasound system has been widely used for examining a woman's uterus. For example, the ultrasound system is utilized in cervical examinations, hysterosalpingography (HSG) and 3D HSG with a saline solution. With the cervical examination that is invasive, it is difficult to investigate the patency of the cervix and an external shape of the uterus. Moreover, the cervical examination may cause perforation, infection or bleeding in the uterus. In case of the HSG there are many problems of causing a pain, using a contrast medium and exposure to radiation. The 3D HSG with the saline solution can be performed non-invasively, and thus, the patients show little rejection. However, the quality of the image obtained by the 3D HSG with the saline solution is degraded in comparison with the images obtained by the cervical examination or the HSG. Thus, it is difficult to discriminate between an inner wall and an inner portion of the uterus, as well as to find lesion with the unaided eye.